Police on Long Island are investigating a violent home invasion the left an elderly couple injured.

It happened around 11:30 p.m Thursday at a home on Roosevelt Avenue in Greenlawn.

Suffolk County police say a man entered the house and demanded cash, credit cards and PIN numbers from the residents -- a 90-year-old pastor and his 75-year-old wife. In fact, the couple was having a Bible study at the house earlier in the evening.

The victims' grandson, Kyle Ashcroft, spoke to Eyewitness News and said the man pushed his way into the house after his grandmother opened the door and immediately stabbed her in the hands.

"The robber came and pushed her to the ground, and she has artificial knees," he said. "He said, 'I need the money,' and she said, 'Well you're going to have to help me up, cause my knees are bad.'"

They then went upstairs, where her husband was watching TV.

"The guy came up to him said, 'You're being robbed,'" Ashcroft said. "My grandfather said, 'Stop, what are you doing?' And then he punched my grandfather in the face. My grandfather is 90 years old. And he stomped on his chest."

Authorities say the suspect then fled the scene with cash and a credit card.

The victims were transported to a local hospital for treatment of non-life threatening injuries.

Ashcroft said someone also stole a church van from just outside the house a few hours before the incident.

"She's not even terrified," he said of his grandmother. "She's just praying for the guy who did this."

The suspect is described as a black male with a thin build, approximately 5-foot-11. He was wearing a dark plaid jacket, dark pants and a scarf over most of his face.

Suffolk County police are offering a $5,000 cash reward for information that leads to an arrest.

"It's really shocking and disturbing to me that someone would push their way into a house and assault these people," Chief Stuart Cameron said. "I mean, if you're going to do it, you certainly did not have to use this level of violence against these people."

Detectives are asking anyone with information about this incident to contact the Second Squad at 631-854-8252, or anonymously to Crime Stoppers at 1-800-220-TIPS.